The present invention relates to an optical switch, and in particular to a segmented Mxc3x97N optical switch.
In the fiber optics industry Mxc3x97N optical switches are used to selectively optically couple one of a plurality of input optical fibers with one of a plurality of output optical fibers. U.S. Pat. No. 4,580,873, issued Apr. 8, 1986 to Frank Levinson, discloses a basic Mxc3x97N optical switch having an array of input lenses along one side and an array of output lenses along another side.
As the demand for the transmission of greater amounts of information grows, so does the number of optical fibers, and so does the size of the switches, which are required to direct the beams of light carrying the information. However, there are definite physical limits within which the design of a switch must adhere. Basic economics dictate that the switch should be as small as possible to minimize material costs, but there are several other interrelated factors that play a role in the design of a switch. These factors include lens characteristics, mirror size, and optical path length. A Gaussian beam launched through an appropriate lens initially converges and subsequently diverges. The minimum beam diameter is called the waste, the position and size of which are based on the parameters of the lens and the beam. The position of the waist is important since the beam diameter increases thereafter, and it is the diameter of the beam that dictates the size of the mirrors and the maximum optical path length to ensure good optical coupling. When all of the lenses have the same focal length, insertion loss is minimized by making the distance from the collimating lens to the reflecting mirror the same as the distance from the reflecting mirror to the focusing lens, and by focussing the beam waist on the reflecting mirror. Obviously, this is impossible for every combination of input and output lens. Accordingly, to minimize the variation in insertion loss, it is important to minimize the variation in the optical path lengths and to position the beam waist at the average optical path length. However, in the conventional matrix switch, the optical path length from the first input port to the first output port is short, while the optical path length from the last input port to the last output port is much longer. Therefore, when conventional switches are used with a large number of input/output ports the variation in optical path lengths is very large, resulting in a large variation in insertion loss.
A previous attempt to equalize all of the path lengths is disclosed in U.S. Pat. No. 5,841,917, issued Nov. 24, 1998 to Jungerman, Roger L. et al. Unfortunately, the arrangement disclosed in the Jungerman et al patent is quite bulky and cumbersome, particularly as the number of input/output ports increases.
An object of the present invention is to overcome the shortcomings of the prior art by providing an optical switch with a minimum insertion loss variation by minimizing the variation in optical path lengths.
Accordingly, the present invention relates to a segmented optical switch comprising:
a first segment including P input ports for launching beams of light into the switch;
a second segment, adjacent the first segment, including X output ports for receiving beams of light from the switch;
a third segment, adjacent the second segment, including Q input ports for launching beams of light into the switch; and
a fourth segment, adjacent the first and third segments, including Y output ports for receiving beams of light from the switch;
wherein the first segment also includes Pxc3x97Y reflecting means for redirecting the beams of light from the P input ports to the Y output ports;
wherein the second segment also includes Pxc3x97X reflecting means for redirecting the beams of light from the P input ports to the X output ports;
wherein the third segment also includes Qxc3x97X reflecting means for redirecting the beams of light from the Q input ports to the X output ports; and
wherein the fourth segment also includes Qxc3x97Y reflecting means for redirecting the beams of light from the Q input ports to the Y output ports.